Operation CASTLE was a six-detonation test series held at the Atomic Energy Commission's (AEC) Pacific Proving Ground in the Spring of 1954. This test series, principally conducted at the Enewetak and Bikini Atolls in the northwestern Marshall Islands, provided proof tests of large-yield thermonuclear, or hydrogen, devices.

CASTLE represented the end of a drive for a workable thermonuclear weapon and the beginning of the refinement of large-H-bombs into smaller and more efficient weapons. After CASTLE, the U.S. could choose in a range of small tactical weapons to large strategic weapons. From this point, weapons development programs concentrated on producing bombs of specific nuclear weapons effects -- heat, blast, and radiation.

The Bravo event of the CASTLE series yielded 15 megatons, unexpectedly the most ever exploded in atmospheric testing by the U.S.. A scientific miscalculation based on a then-unknown "tritium fusion bonus" of highly enriched lithium-6 contributing the the detonation yield caused the yield to be about two and a half times of that what was expected.

Reports indicate that Bravo was the single worst incident of fallout exposure in all of the U.S. atmospheric testing program. Despite winds in an acceptable flow zone, the greatly unexpected yield caused a much larger mushroom than originally calculated, causing a much wider and massive accumulation path of fallout danger. Fallout was scattered over more than 5,000 square miles of ocean and islands, resulting in the contamination and exposure of military, civilian U.S. personnel working on the shot, and people of the islands who were earlier moved to a supposedly "safe" island but received large amounts of radiation. Acute radiation effects were observed among some of these people.

The supreme commander of Joint Task Force 7 was Major General Percy Clarkson, who gave this report to top secret oversight committees of U.S. Congress. General Clarkson was the U.S. Army's 33rd Division commander (October 1943 - November 1945) in the raging battles of the Philippines during the Second World War.

The shots in the CASTLE series were:

Bravo, February 28, Bikini, 15 megatons
Romeo, March 26, Bikini, 11 megatons
Koon, April 6, Bikini, 110 kilotons (sanitized out of the film as a fizzle of 1 megaton predicted yield)
Union, April 25, Bikini, 6.9 megatons
Yankee, May 4, Bikini, 13.5 megatons
Nectar, May 13, Enewetak, 1.69 megatons

Opening narration: Carey Wilson

Wilson was a very influential producer and scriptwriter in Hollywood -- principally with MGM -- and led a double life role as a "Q-Clearance" presenter and contributing scriptwriter in top secret films produced by the Atomic Energy Commission and the Armed Forces Special Weapons Project (AFSWP).

Q-Clearance was a top secret classification within the Atomic Energy Commission, later renamed to the Department of Energy.

Weapons development narration: Dr. Alvin C. Graves, Scientific Commander, J-Division (weapons testing), Atomic Energy Commission

Related sites:

http://www.archive.org/details/ExerciseDesertRock1951

http://www.archive.org/details/OperationGreenhouse1951

http://www.archive.org/details/TumblerSnapper1952

http://www.archive.org/details/OperationIVY1952

http://www.archive.org/details/The280mmGunattheNevadaProvingGround1953

http://www.archive.org/details/MilitaryEffectsStudiesonOperationCastle1954

http://www.archive.org/details/MilitaryEffectsonOperationRedwing1956

http://www.archive.org/details/OperationDOMINICNuclearTests1962

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